Loudoun, Fairfax, and Arlington counties, all in Virginia, swept the top three spots. All three counties have household incomes of more than $100,000.

Loudoun County took the top spot, with a median household income of $119,134 in 2011.

Howard and Prince William counties in Maryland, and Fauquier and Montgomery counties in Virginia, were also in the top 10.

The counties surrounding D.C. have the benefits of low unemployment and a lot of dual-income households, as well a thriving business-service sector, according to The Washington Post. The area also rebounded well from the recession, and has the highest amount of adults with a college degree in the country.